Effects of quantum mechanical tunneling on rates of radiative association

Radiative association in ion-molecular collisions plays an important role in the synthesis of polyatomic species in interstellar clouds. Here, the results of calculations on the radiative association reactions C(+) + H2 - CH2(+) + h(nu) and CH3(+) + H2 - CH5(+) + h(nu) are presented. While these calculations are based on the treatment of collisionally stabilized associations of neutral free radicals originally proposed by Troe, the effects of quantum mechanical tunneling through the centrifugal barriers on the effective potentials are included in the calculations for the first time. At 10 K, the inclusion of tunneling is estimated to increase the rates of association by factors of 2.2 for C(+) + H2 and by 2.0 for CH3(+) + H2.